Benefit Plans - Contribution and Benefit Payment Expectations (Details) (USD $) In Millions	Jun. 30, 2011
Contribution and benefit payment [Line Items]
2011 expected contributions, top of range	$ 350
2011 expected contributions, bottom of range	$ 300

Name:

pgn_DefinedBenefitPlanEstimatedFutureEmployerContributionsInNextFiscalYearBottomRange

Namespace Prefix:

pgn

Data Type:

xbrli:monetaryItemType

Balance Type:

debit

Period Type:

instant